Carboxylic Acid Functional Group

Carboxylic acids are organic compounds (hydrocarbons) that
contain the element oxygen. We've already encountered organic
compounds containing oxygen those were called alcohols and
ethers. Carboxylic acids are different from alcohols and ethers
in that the oxygen interacts with carbon differnetly than in the
case of alcohols and ethers. In carboxylic acids there are TWO
oxygen atoms bonded to the carbon atom. One of the oxygen atoms
double bonds to the carbon the other is a single bond. What does
this carboxylic acid functional group look like?

Functional Group

Lewis Structure

Electron-dot Structure

Condensed Formula

Carboxylic acid

-COOH

Notice there are four bonds to the carbon atom and two bonds
to each of the oxygen atoms in this functional group.

The simplest carboxylic acid is formic acid, HCOOH. The
structure of formic acid is shown below.

Ball-and-Stick

Lewis Structure

Electron-dot Structure

Formic acid is secreted by ants when they bit human beings.
Most of us probably recall how uncomfortable an ant bit is.

The carboxylic acids have much different formulas compared to
alcohols or ethers. Notice the carboxylic acid has an -OH group
just like the alcohols, but in the case of the carboxylic acid
the -OH group is bonded to a carbon double bonded to another
oxygen atom. In the case of the alcohol the -OH group is bonded
to a carbon with hydrogen atoms only.

The next simple carboxylic acid is acetic acid.

Ball-and-Stick

Lewis Structure

Electron-dot Structure

Acetic acid is the important ingredient of vinegar. We use
vinegar to clean and we also ingest vinegar. It is found in salad
dressings. We can even find flavored vinegars that are excellent
for cooking.

What are some other interesting compounds which contain
carboxylic acid groups? Carboxylic acids are acids just as the
name indicates. Acids taste sour and carboxylic acids add the
sour taste we are all most familiar with in foods. Carboxylic
acids are also found in fats. So lets look at some examples of
common carboxylic acids.

Compound

Ball-and-Stick

Lewis Structure

benzoic acid (found in berries)

steric acid (animal fat)

Some other examples of compounds with carboxylic acid
functional groups contain some other functional groups. Citric
acid is the carboxylic acid found in citrus fruits, lactic acid
is found in sour milk and is produced by the body during
exercise, and tartaric acid is found in fruit, wine and grape
juice.